1. Technical Field
The present invention relates to a proximity-type imaging device that is provided with an angle limiting filter that limits an incidence angle of light transmitted from the subject to an image sensor on a front face of the image sensor so as to be able to capture a subject, which is in proximity to the image sensor, and more particularly, relates to a proximity-type imaging device that captures a subject with the subject being in substantially close contact with an image sensor and an angle limiting filter for use therein.
2. Description of the Related Art
Image scanners that capture subjects such as an image and a document to acquire digital images have been widely used. As the image scanners, there are an image scanner in which a subject image is reduced by a reduction optical system so as to form an image on an image sensor and another image scanner that brings an image sensor to be in proximity to a subject so that the image sensor is in substantially close contact with a subject captures the subject by.
Recently, there are cases where such image scanners are built into a small-sized thin-type device such as a portable cellular phone or a notebook personal computer. Therefore, decrease in size and thickness of the image scanners has been demanded. An image scanner using the reduction optical system can reduce the size of the image sensor. However, since the image scanner uses a reduction optical system in which plural lenses are disposed along an optical axis direction, there is a limit to decrease the size and the thickness of the image scanner. On the other hand, an image scanner of the proximity-type needs an image sensor having substantially the same size as that of a subject. However, the image scanner of the proximity-type can be easily formed to be thinner than the image scanner using the reduction optical system. Accordingly, mainly the proximity-type image scanners are built into small-sized thin-type devices.
The proximity-type image scanners captures a subject with bringing the subject and the image sensor into substantially close contact with each other and establishing one-to-one correspondence between respective portions of the subject and light receiving areas, which are formed of plural pixels and are partitioned on a light receiving surface. However, the image sensor and the subject are not completely brought into close contact with each other, and there is a small gap therebetween. In the proximity-type image sensors, light transmitted from the respective portions of the subject is incident not only to the corresponding areas but also to a peripheral area thereof. Accordingly, it is difficult to acquire a fine image. Therefore, in the proximity-type image scanners, it is required to limit the incidence angle of light, which is incident to the image sensor.
As an example of limiting the incidence angle of light which is incident to the image sensor as described above, there has been known an example in which a lattice shaped light-shielding filter that shields boundaries of the light receiving areas in a compound-eye imaging device, in which lenses are arranged in a planar shape so as to correspond to the light receiving areas (JP 2005-31460 A). Also, there has been known an example in which a rod lens having a cylinder shape having a refractive index which decreases from the center thereof toward the periphery thereof is arranged or a film camera in which a porous plate having plural through holes disposed therein.
As described above, the imaging filter that is used for limiting the incidence angle of light being incident to the image sensor is formed in a lattice shape so as to substantially match with the light receiving areas. However, as the size of the light receiving areas decreases, for example, as in the case where each pixel is associated with a corresponding portion of a subject, it is difficult to provide a through hole mechanically on a substrate or to manufacture a rod lens having the same size as that of the pixel. Accordingly, recently, as fine capturing is required while an image scanner is made small and the light receiving areas are made small, an imaging filter in which a light shielding film having openings corresponding to the light receiving areas is provided on a surface of a glass substrate is used.